Engine systems in vehicles may be designed to utilize smaller amounts of fuel during idle conditions. These smaller amounts of fuel may be further reduced by prudently managing electrical loads during idle as well as by using alternators with higher efficiency. Further still, by generating electrical power from regenerative braking instead of combusting fuel for operating an engine-driven electrical generator, fuel quantities may be additionally diminished during idling.
As fuel consumption during idle is reduced, a corresponding decrease in intake air flow may be desired. As such, intake air flow during idle may be actively regulated via an electronic throttle in an engine intake. However, passive devices in the engine system may also affect engine air flow during idle. For example, vehicle systems may include one or more aspirators coupled in the engine system to harness engine air flow for generating vacuum. Motive flow through the one or more aspirators may bypass the electronic throttle and flow into the engine intake. In another example, blow-by gases in a crankcase may be received in the engine intake during idle via a crankcase ventilation (CV) system including a passive crankcase ventilation (CV) valve. Specifically, blow-by gases may flow through a smaller annular opening (e.g., a low flow orifice) in the CV valve even though the CV valve is substantially closed during idle.
The inventors herein have recognized the above issue and identified an approach to at least partly address the issue. In one example, a method for a boosted engine comprises adjusting, via an electronic controller, an opening of a common shut-off valve (CSOV) based on engine idling conditions, and each of a motive flow through an aspirator and a crankcase ventilation flow from a crankcase, the motive flow and the crankcase ventilation flow combined together and flowing through the CSOV when the CSOV is open. In this way, air flow from passive devices such as the CV valve and the aspirator can be significantly reduced during engine idle.
For example, a boosted engine system may include a compressor coupled in an intake passage and an aspirator coupled in a bypass passage. The bypass passage may be fluidically coupled at a first end to the intake passage upstream of the compressor. Further, a second end of the bypass passage may be fluidically coupled to an intake manifold of the boosted engine via a common shut-off valve (CSOV). A crankcase of the boosted engine system may be fluidically coupled to the intake manifold via a conduit. The conduit may enable evacuation of blow-by gases via a passive crankcase ventilation (CV) valve. The conduit flowing CV gases and the bypass passage flowing aspirator air flow may intersect upstream of the CSOV. As such, motive air flow received via the aspirator and blow-by gases from the crankcase may be combined together and a mixture of motive air flow and blow-by gases may stream through the CSOV, when open, into the intake manifold. Further, the CSOV can modulate air flow from each of the aspirator and the crankcase into the intake manifold. An engine controller may be configured to adjust a position of the CSOV based on engine conditions. Specifically, the CSOV may be adjusted to close (e.g., fully close) when the engine is idling. By closing the CSOV, the flow of air from the aspirator and blow-by gases from the crankcase into the intake manifold may be simultaneously stopped.
In this way, engine air ingestion during idle conditions may be reduced. Specifically, air ingestion from passive devices such as a CV valve and/or an aspirator may be substantially decreased during engine idling allowing a significant decrease in a rate of fuel consumption. By employing a common shut-off valve to regulate both air flow received from the aspirator and blow-by gases from the CV valve, a simpler control algorithm for the shut-off valve may be deployed. A serendipitous benefit of using the common shut-off valve may include utilizing aspirators with higher motive flow rates for increased vacuum generation. Further, the presence of the CSOV may also enable an increase in the size of a low flow orifice in the CV valve. By increasing the size of the low flow orifice, a higher evacuation rate of blow-by gases may be achieved when the common shut-off valve is open and manifold vacuum is deeper. Overall, engine performance may be improved while lowering operational costs due to the reduction in fuel consumption.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.